Security Flaw in Simple Generalized Group-Oriented Cryptosystem Using ElGamal Cryptosystem

Article type: Research Article

Authors: Li, Chuan-Ming | Hwang, Tzonelih | Lee, Narn-Yih

Affiliations: Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan, Taiwan 701, R.O.C., e-mail: licm@ismail.csie.ncku.edu.tw, hwangtl@ismail.csie.ncku.edu.tw | Department of Information Management, Southern Taiwan University of Technology, Tainan, Taiwan 710, R.O.C., e-mail: nylee@mail.stut.edu.tw

Abstract: A generalized group-oriented cryptosystem (GGOC) based on ElGamal cryptosystem was proposed by Yang et al. in 2003. This study shows that if the authorized decryption sets of users are not properly predetermined in Yang et al.'s GGOC, an unauthorized decryption set of users can recover the encrypted message without difficulty. This study also presents an improved protocol to resist such an attack.

Keywords: generalized group-oriented cryptosystem, access structure, security

Journal: Informatica, vol. 18, no. 1, pp. 61-66, 2007